Rotary operable devices are well known, as are rotary operators for operating such devices are well known. Examples are rotary switches and valves comprising a manually operable rotary operator such as a handle grip, a knob or a lever. A particular class of rotary operators is formed by safety rotary operators in which the device may be blocked from unintended operation by locking the operator in a particular position (safe position) corresponding to a particular state of the device, e.g. an “off” state.
However, dangerous situations may arise in case the operator can be locked in a “safe” position whereas operational portions of the device are not in the corresponding desired state. For instance, in some rotary electrical switches having stationary electrical contacts and rotary electrical contacts mounted to a spindle, the contacts may have become welded together in an “on” state whereas the rotary operator may be turned and locked in a position corresponding to an off-state with torsion of the spindle. Thus, the switch may appear to be “off” whereas in fact the electrical circuit is still “on”. Similar may happen for other types of rotary operable devices and for rotary valves wherein the actual position of an operated object, e.g. a switch or a valve body, may not correspond to the position of the object indicated by the position of the operator.
For example, U.S. Pat. No. 5,302,925 discloses a molded case circuit breaker rotary handle operator which allows the circuit breaker handle to be locked when the circuit breaker contacts are open. The handle is prevented from being locked in position when the circuit breaker contacts are welded in their closed condition since a padlock plate extending from the rotary handle is prevented from operation unless the circuit breaker contacts are open.
EP 0 450 699 discloses a locking device comprising within a handle for rotating control of electromechanical equipments a latch, for locking the handle in a preselected position, which can be engaged by a padlock only if the electromechanical equipment properly carries a desired movement out, making available in the latch a seat for the padlock only in the last case, the possibility of the latch of being engaged by the padlock depending either by movement clearance between the handle and rotating movement control devices thereto connected, or by movement clearance between a shaft integrally connected to the handle and a disk, provided with cam shape, controlling an enabling device.
DE 42 06 378 discloses an actuator for switch devices which has a rotating handle form-fitted to the switch shaft of the device in the rotary direction, and snap-fitted on to the shaft in the axial direction. The handle has a pivot lever. In the closed position, this blocks movements of the handle and also prevents pulling of the switch shaft. The lever has a nose which engages on a radial aperture in the shaft. Rotary movement is locked by a locking device or a recess in the housing wall. Closure or sealing devices can be inserted in apertures of the lever to protect against unauthorised operation.
Such devices comprise a significant number of parts, making them rather complex and costly to manufacture and they are correspondingly sensitive to damage and malfunction, e.g. by rough handling and/or soiling in outdoors field-operation.
Since safety is of the utmost importance and cost efficiency is always a concern, there is a desire for an improved rotary operator.